Injection phase locking device in an fm-transmitter for a self-oscillating oscillator modulated by a modulation signal

ABSTRACT

A phase locking arrangement in which a free-running oscillator running with a frequency fo is injection phase locked by a synchronizing oscillator with a free-running frequency fs and a multiplier giving a multiplied frequency n . fs. A modulating frequency fm modulates both the free-running oscillator and the synchronizing oscillator through two direct coupled FMmodulators, so that the free-running oscillator will be continuously tuned to a frequency f1 which is chosen so that the synchronizing band Delta f f1 - fo of the free-running oscillator is narrow, so that the synchronizing power from the synchronizing oscillator can be kept low.

United States Patent 1191 Endersz June 5, 1973 s4 INJECTION PHASELOCKING DEVICE 3,118,117 1/1964 1011 3;, IN AN FM TRANSMITTER FOR A3,566,269 2/1971 Wa er....

3,437,958 4/1969 Shaw ....32s/14s SELF'OSCILLATING OSCILLATOR 3,324,4146/1967 Numakura ..325/47 MODULATED BY A MODULATION SIGNAL Inventor:'Gyorgy Geza Endersz, Hagersten,

Primary Examiner-Howard W. Britton [75] Attorney-Frederick E. Hane,Charles E. Boxley Sweden and Cami] P. Spiecens [73] Assignee:Telefonaktiebolaget LM Ericsson, ABSTRACT Stockholm Sweden A phaselocking arrangement in which a free-running [22] Filed: July 2, 1971oscillator running with a frequency f is injection phase locked by asynchronizing oscillator with a free- [21] PP 159,327 running frequencyf, and a multiplier giving a multiplied frequency n f,. A modulatingfrequency f,, [30] Foreign Application Priority Data modulates both thefree-running oscillator and the synchronizing oscillator through twodirect coupled July 10, 1970 Sweden ..9580/70 FMqnodulato -s, so thatthe free-running oscillator will be continuously tuned to a frequency fwhich is [52] US. Cl. ..325/l48, 325/105, 325/126, chosen so that thesynchronizing band Af=f f,, of 325/184, 332/22 the free-runningoscillator is narrow, so that the [51] Int. Cl. ..H03c 3/02, 1104b 1/04,H04b l/66 synchronizing power from the synchronizing oscillator [58]Field of Search; ..325/184, 145, 146, can e ept low- [56] ReferencesCited 8 Claims, 6 Drawing Figures UNITED STATES PATENTS I 2,691,09510/1954 Bailey ..325/146 MULTIPLIER -/"/'U '05 SYNCHRONIZER /r 5 \LOAD 10 MODULATOR 7 0 7 f1 7 l OSCILLATOR I MODULATOR EEKEE Z B CQ SIGNALSOURC v T t E r l PM June 5, 1973 i 2 Shah-Shoot 1 f1 5) -OS is n '0SYNCHRONIZER/ f OSCILLATOR -LOAD Fly.

7 PRIOR ART INVENTOR Gvis'nfl ian Emu-n8:

ATTORNEYS INJECTION PHASE LOCKING DEVICE IN AN FM-TRANSMITTER FOR ASELF-OSCILLATING OSCILLATOR MOUULATED BY A MODULATION SIGNAL The presentinvention relates to an injection phase locking arrangement in anFM-transmitter for a freerunning oscillator modulated by a modulatingsignal. More precisely the arrangement comprises a phase lockingarrangement for FM-transmitters within the microwave range, which allowsa reduction of the power necessary for the phase locking.

One solution for phase-locking free-running oscillators has previouslybeen described in an article by R. Adler; Proceedings of IRE, June 1946,p. 351-357, according to which a free-running oscillator may be phaselocked by means of a controlling signal differing in frequency from thefree-running frequency of the oscillator by a value of Af, the frequencydifference being dependent on the relation between the power of thecontrolling signal and the oscillator signal.

An object of the present invention is to provide a phase-lockingarrangement, particularly for an FM- modulator in microwave FM-systems,using such principle but also causing an increase of the frequencydifference with a maintained power synchronization.

The characteristics of the arrangement will appear from thecharacterizing part of the main claim.

The most important use of the arrangement is for the phase-locking offree-running semi-conductor oscillators within the microwave range, e.g.domain-, LSA and avalanche oscillators, having the most unfavorablenoise frequency relation near the carrier frequency (free-runningfrequency).

The invention will be described in more detail with reference to theaccompanying drawings, in which FIG. 1 shows examples of thephase-locking of an oscillator according tothe earlier known principle.

FIG. 2 shows a noise-frequency diagram when phaselocking a free-runningoscillator by means of a synchronization signal.

FIG. 3 shows a diagram with a logarithmic scale, in which the graphicalrepresentation of the function JP. /2 f Q) running frequency f of theoscillator is reduced to the noise level of the synchronizationoscillator, which may be lower than that of the free-running oscillator,if the synchronization oscillator e.g., consists of a quarts crystalrunning with a frequency f,. Line 1 then represents the frequency noisecharacteristic for a free-running oscillator, e.g. a semi-conductoroscillator, line 2 represents the characteristic for a low noiSesynchronization oscillator, e.g., a crystal oscillator the frequency ofwhich is multiplied and the curve 3 represents the characteristicobtained when the free-running oscillator is phase-locked to thesynchronization oscillator. It appears from the figure that thesemi-conductor oscillator (which gives a considerably higher power thanthe crystal oscillator) by the phase-locking has obtained the favorablenoise qualities of the crystal oscillator within the synchronizationband Af around the center frequency f Applied to microwave FM-systemsthe center frequency f, may be of the magnitude 10 GHz and the frequencyf in the intermediate frequency range e.g. 100 MHz and therefore it isnecessary to make a frequency multiplication by n, where n may be aninteger chosen in a suitable manner, the result being f n -f Thefrequency band in which it be desired that the oscillator issynchronized is the so called synchronization band Af, which is thedifference -f between the free-running frequency of the oscillator andthe frequency of the synchronizer.

According to the above mentioned article there is a definite relationbetween P /P and Af:

where Q is the figure of merit of the oscillator. The function:

P ,,/P (f /2 Af' Q) 2 is in FIG. 3 plotted for various values of thefactor of merit Q of the oscillator.

From the above it is apparent that if the synchronization band Af isincreased, also the synchronization power P must be increased. If Af isincreased, which is the case upon frequency modulation (FM), autor naticfrequency regulation (AFC) or frequency which is stated in the abovementioned article by Adler is plotted for different values of theparameter Q.

FIG. 4 shows in the form of a block diagram the principle of theinvention.

FIG. 5 is a circuit diagram of an embodiment of the invention.

FIG. 6 shows a practical realization of an embodiment according to FIG.5.

The previously known solution for phase-locking a free-runningoscillator, described in the article by Adler, PIRE, June 1946, is shownin FIG. 1. The oscillator OS runs with the frequency f and supplies aload LO with the power P,,. If the long time-or short time stability(frequency noise) is more unfavorable than desired, or if a close phasecontrol of the oscillator frequency is wanted, a synchronizer SY isused, e.g. a crystal oscillator, which is connected to the oscillatorOS. The synchronizer SY transmits a signal to the oscillator OS with thefrequency f, and with the power P,. FIG. 2

shows anoise-frequency diagram for a device of the above mentioned type.It has been found that the noise level within a band-width of 2 Afaround the freechange of the oscillator, a higher synchronization powerP is required.

The principle of the invention is shown in FIG. 4. A

direct modulator M01 is connected to the synchro nizer SY and a directmodulator M02 is connected to the oscillator OS. The direct modulatorsare both controlled by a modulating signal from a signal source M, whichgenerates an output signal with the voltage U,, and the frequencyf Theunit M may e.g., be the transmitter in a radio relay link (e.g. a radiorelay link for telephone video bands in a picture telephone apparatus)and the load LO supplied by the oscillator OS may consist of atransmitting antenna. The frequency f will modulate the frequency f, andthe frequency f and the relation between the voltage U and thefrequencies f, and )2, respectively constitutes the modulationcharacteristic for the modulators M01 and M02 respectively. Themodulators are in a known manner so arranged and the modulationcharacteristic so chosen, that the modulator MOI will modulate thesynchronization unit SY within a smaller frequency band (modulationband) than the band within which the modulator M02 modulates theoscillator OS. The frequency f, of the synchronizer will e.g., vary i 50kHz around its synchronization frequency .MI-Iz, while the oscillator OSis' modulated within a frequency band of 4.5 MHz around its free-runningfrequency f, 10 GI-Iz. After a frequency multiplication of n 100 bymeans of a multiplier unit MU, a signal with the frequency f n -j100(100 i 0.05) 10 GI-lz i 5 MHZ is supplied to the oscillator 08. As aresult the synchronizer SY will modulate the oscillator so that it willbe tuned to a frequen y f n fl, continuously. The synchronization bandAf= (f n 5.) will consequently be kept narrow all the time. It will thenbe possible to keep the synchronization power P as low as sufficient forsuppressing the frequency noise of the oscillator near the frequency f,(compare FIG. 2). The synchronization power P may be reduced so muchthat it corresponds to the characteristic of the modulator M01 and byfor example about 20 dB in ordinary microwave FM-systems. This can beunderstood from FIG. 3. Without the modulator. M02 the frequencydifference form the multiplier will be 10 GHz i 5 MHz, i.e., asynchronization band of about MHz is required. If, however, theoscillator OS is modulated, its free-running frequency f,, will bedisplaced 4.5 MHz at a maximum frequency difference 5 MHZ),- the resultbeing that in this case a synchronization band of only 1 MHz will berequired. If the Q-value of the oscillator is 50 (a common value in thisconnection) it can immediately be seen from FIG. 3 that the value of PlP is increased by dB or, vice versa, that P /P, is reduced by 20 dB. Pbeing the constant output power from the oscillator there will be areduction in P of 20 dB. By connecting a temperature sensing device T tothe modulator M02, a simple compensation of the temperature drift of theoscillator is also made possible.

Instead of using a multiplier a mixer stage could be used. As known,this mixer stage consists of a frequency mixer and a local oscillator.The two FM- modulators M01 and M02 are in this case arranged so thatthey have the same modulation characteristic.

FIG. 5 shows a circuit diagram of the connection of the oscillator tothe other units through high frequency transformers Trl, Tr 2. Theoscillator is built up as a series connection of a negative impedanceelement R in series with a resonant cavity K. A varactor diode or aYIG-resonator connected to the oscillator cavity via a high frequencytransformer Trl can be used as direct modulator M02. The modulator M01,the synchronizer SY and the multiplier unit MU each consists of knowncircuits within the intermediate frequency range and therefore theirconstruction will not be described in detail.

FIG. 6 shows the practical construction of the direct modulator M02 andthe oscillator OS. The impedance supplied to the oscillator. The' loadLO in this case consists of a transmitting antenna. The free-runningfrequency f, of the oscillator is of the magnitude 10 GHz. As appearsfrom FIG. 2 the frequency noise of the output signal within thesynchronization band Af is determined by the noise qualities of thesynchronization signal. Outside of the synchronization band the noiselevel is higher, depending on the noise from the feedback loop of theoscillator and the multiplier, and here the noise qualities aredetermined by the cavity oscillator itself. The noise spectrum of thefree-running Gunn oscillator is reduced by about 9 dB/octave from thefreerunning frequency f,,, while for ordinary negative resistanceoscillators the value is about 6dB/octave.

The principle of the present invention may be used inall kinds ofoscillator transmitters for communication systems and is no restrictedto the disclosed examples.

I claim:

1. An FM-transmitter comprising a modulating signal source, asynchronization oscillator, a frequency changing means for changing thefrequency of the signal from said synchronization oscillator, afree-running oscillator, means for connecting said frequency changingmeans to said free-running oscillator so that the signal generated bysaid free-running oscillator is phaselocked to the signal generated bysaid synchronization oscillator, a modulating signal source forgenerating a modulating signal, a first FM-modulator means connected tosaid modulating signal source for frequency modulating the signalgenerated by said synchronization oscillator in accordance with thevalues of the modulating signal, a second FM-modulator means connectedto said modulating signal source for frequency modulating thephase-locked signal generated by said free-running oscillator inaccordance with the values of the modulating signal, and a load meansconnected to said free-running oscillator for receiving the modulatedand phase-locked signal from said free-running oscillator. Y

2. The FM-transmitter of claim 1 wherein said frequency changing meansis a frequency multiplier.

3. The FM-transmitter of claim 6 wherein the modulation characteristicsof said FM-modulator means are chosen with respect to each other so thatthe modulation bandwidth of said first FM-modulator means is less thanthe modulation bandwidth of said second FM modulator means.

4. The FM-transmitter of claim I further comprising a temperaturesensitive means connected to said second FM-modulator means forcompensating any temperature sensitive frequency drift of saidfree-running oscillator.

5. The FM-transmitter of claim 1 wherein said frequency changing meanscomprises a mixer driven by a local oscillator.

6. The FM-transmitter of claim 5 wherein said FM- modulator means havethe same modulation characteristics.

7. The FM-transmitter of claim 1 wherein said free running oscillatorcomprises a resonant cavity and a Gunndiode connected within saidcavity.

1 8. The FM-transmitter of claim 7 wherein said second FM-modulatormeans comprises a varactor diode.

1. An FM-transmitter comprising a modulating signal source, asynchronization oscillator, a frequency changing means for changing thefrequency of the signal from said synchronization oscillator, afree-running oscillator, means for connecting said frequency changingmeans to said free-running oscillator so that the signal generated bysaid free-running oscillator is phaselocked to the signal generated bysaid synchronization oscillator, a modulating signal source forgenerating a modulating signal, a first FM-modulator means connected tosaid modulating signal source for frequency modulating the signalgenerated by said synchronization oscillator in accordance with thevalues of the modulating signal, a second FM-modulator means connectedto said modulating signal source for frequency modulating thephase-locked signal generated by said free-running oscillator inaccordance with the values of the modulating signal, and a load meansconnected to said free-running oscillator for receiving the modulatedand phase-locked signal from said free-running oscillator.
 2. TheFM-transmitter of claim 1 wherein said frequency changing means is afrequency multiplier.
 3. The FM-transmitter of claim 6 wherein themodulation characteristics of said FM-modulator means are chosen withrespect to each other so that the modulation bandwidth of said firstFM-modulator means is less than the modulation bandwidth of said secondFM-modulator means.
 4. The FM-transmitter of claim 1 further comprisinga temperature sensitive means connected to said second FM-modulatormeans for compensating any temperature sensitive frequency drift of saidfree-running oscillator.
 5. The FM-transmitter of claim 1 wherein saidfrequency changing means comprises a mixer driven by a local oscillator.6. The FM-transmitter of claim 5 wherein said FM-modulator means havethe same modulation characteristics.
 7. The FM-transmitter of claim 1wherein said free-running oscillator comprises a resonant cavity and aGunndiode connected within said cavity.
 8. The FM-transmitter of claim 7wherein said second FM-modulator means comprises a varactor diode.